Inductors are known to be critical energy storage components of power conversion circuits located on integrated circuit chips. By way of one example, a thin-film ferromagnetic inductor may be used for on-chip DC-DC voltage conversion on a computer processor.
Such inductors have typically been formed by creating a magnetic material stack that is comprised of multiple layers of magnetic material. The magnetic material stack serves as the yoke material for the inductor, around which one or more coil windings or wires (e.g., single-turn and multi-turn coil designs) are wrapped. In the thin-film ferromagnetic inductor, the stack may be several microns or more in thickness. The overall thickness of the stack is selected to obtain a desired inductance value, while maintaining a desired operating frequency.
While increasing the thickness of the magnetic material stack increases the inductance value, it also increases eddy currents. An eddy current is an electrical current that is induced within a conductor by a changing magnetic field in the conductor. The induced electrical current creates a magnetic field that opposes the magnetic field that created the induced current, which adversely affects the performance of the inductor. Thus, controlling the thickness of the magnetic material stack is beneficial to the performance of the inductor. However, at micron-level stack sizes, such control is a significant challenge.